This invention relates generally to imaging methods and apparatus, and more particularly, to methods that provide for improvements in x-ray detector fabrication and resulting apparatus.
X-ray detectors typically include a photodiode portion and a scintillator portion. An x-ray enters the detector and impinges the scintillator material, wherein photons of visible light are created. The visible light then leaves the scintillator material and impinges a photodiode. The photodiodes are polled, returning attenuation measurements. This data is then used to create images. Each scintillator pixel has a corresponding photodiode, and it is desirable that all light generated in the scintillator be directed toward the photodiode, therefore reflective material is used to reflect light directed in directions other than the photodiode direction. In other words, one can imagine a scintillator cell as a six sided cube, with one side facing the photodiode and the five other sides having reflective material. The side opposite the photodiode is termed the top side.
One known scintillator array (commonly called a “cast pack”) used in Computed Tomography (CT) uses a cast reflector coating as its light reflector. The reflector is epoxy filled with a highly reflective powder such as TiO2. The cast reflector coating typically mechanically bounds the scintillator pixels together to form an array and the cast reflector coating also reflects the light back into the pixels from the surface. This reflector is important for light collection efficiency purposes. One problem in the known reflector process is the curing shrinkage of the epoxy and the thermal expansion mismatch between the reflector and the ceramic scintillator pixels. The reflector has about 70% to 80% epoxy in volume. After curing, the epoxy will shrink by more than 5% in volume. While it shrinks, the adhesion is already being developed between the ceramic and reflector. This shrinkage causes very high stress on the interface and also inside the ceramic pixels. This stress can lead to cracks of the ceramic pixels, and delamination between the reflector and ceramic pixels. A wire saw is typically used to perform geometric dicing and pixelating of the packs before the casting, and this shrinkage problem becomes more damaging. The curing stress can cause the packs to bow along both the X and the Z directions. This in turn can cause the pixels to tilt and can cause pixel misalignment. The bowing can also cause other process related problems because of the lack of the flatness of the packs.
Therefore, below are described methods and apparatus that at least partially solve the above described problems.